There are generally two types, one is iron, which is carbon steel. One is stainless steel, and of course there are copper and aluminum nuts, but these are less used. Copper is still useful, and nuts like aluminum are rarely used. There are two types of hex nuts, one is 4.8, the normal nut, and the other is the 8-level nut. For more information on the industry of nuts, read the nut specification sheet and the nut industry national standard specification sheet. These nut specifications and industry standard knowledge. Can give us a deeper understanding of the nut.